This invention relates to a process in which polyurethane waste materials and/or polyurethane reject goods may be transformed into useable polyisocyanates. Specifically, the present invention relates to a process in which a liquid mixture of a polyisocyanate and such polyurethane waste material which may be used in the production of polyurethanes is produced.
As the polyurethane manufacturing industry grows, the problem of removing and re-using polyurethane waste materials or reject goods becomes increasingly significant. Flocks of flexible polyurethane foam have been bonded together to form composite bodies but only small quantities of flexible foamed plastic materials may be used in this manner. Waste semi-rigid and rigid polyurethane foams and elastomer granulates cannot, however, be employed in this manner. Consequently, large quantities of polyurethane waste goods and reject goods from rigid and flexible foam production and from elastomer production have to be dumped or destroyed at special refuse facilities. These methods of disposal are undesirable, however, because they create considerable ecological, technical and economic problems due to the low specific weight and the large volume of the waste or reject goods. Therefore, for ecological and economic reasons, there is a considerable interest in economically re-using the constantly increasing quantities of polyurethane waste materials.
German Offenlegungsschriften Nos. 2,362,919; 2,362,920 and 2,362,921 disclose processes for hydrolyzing waste materials from polyurethane foams at elevated temperatures using steam. However, these processes require high temperatures and pressures (for example 240.degree. C. and 40 atm.) which means that the dissociation of the polyurethane wastes can only be performed with expensive equipment and at high costs. Furthermore, the reaction products precipitate in mixture with water and have to be separated through special processes prior to re-use.
It is furthermore well-known (German Offenlegungsschrift No. 2,238,109) to degrade polyurethane foam wastes into re-foamable polyols by heating them to 175.degree. to 250.degree. C. in high boiling dihydroxy compounds, preferably diethyleneglycol and advantageously in the presence of about 10% of a diethanol amine. By reurethanizing in this manner, short-chained polyols are obtained, which can only be used advantageously for the production of rigid polyurethane foams. According to the theory of the cited Offenlegungsschrift, this process is preferably only used for the dissociation of rigid polyurethane foam. Another disadvantage of this process is that the reaction is complete only after several hours. The process therefore requires a lot of energy and is difficult to transfer to continuously operating plants.
It is known from the German Offenlegungsschrift No. 2,035,175, especially from Examples 10 to 14, to dissolve polyurethane wastes in monomer diisocyanates at about 140.degree. to 160.degree. C. and to use these solutions as isocyanate components in the production of polyurethane plastics. As the mentioned embodiments of the German Offenlegungsschrift No. 2,035,175 and the comparison examples given below show, the production of these solutions is very time consuming and consequently requires a high amount of energy. Further, an appreciable degradation of the polyurethane wastes does not take place. Consequently, the solutions of German Offenlegungsschrift No. 2,035,175 are comparatively highly viscous mixtures which are of limited value in the production of polyurethane plastic materials. Moreover, highly branched polyurethanes may not be dissolved according to the process of this German Offenlegungsschrift. The highly viscous solutions which are initially produced also often have the serious disadvantage of solidifying after being stored for a short time at room temperature (in this connection, see the following Examples 1 to 5, and the corresponding Comparative Examples).
It would therefore, be advantageous to provide a process which permits re-use of polyurethane waste materials or polyurethane reject goods, without the disadvantages of these prior art processes.